Surface rewinding machines are currently used to produce logs of web material, in particular, although not exclusively, paper such as tissue paper, for example toilet tissue, kitchen paper and the like. In these machines the log being formed is made to rotate through the effect of winding members in peripheral contact with the log. Typically, these winding members are rollers or, in some cases, belts or combinations of rollers and belts.
Surface winding machines may be of the continuous type, that is in which the web material is fed continuously and at an essentially constant speed, even during the exchange phase. This is the phase during which the web material is severed, the completed log is unloaded from the winding cradle and winding of a new log commences in the winding cradle. Surface winding machines can also be of the start-stop or discontinuous type. In this type feed of the web material is interrupted during the exchange phase.
The logs formed in rewinding machines are subsequently cut into rolls of a smaller axial length and these are packaged, normally in multiple packages, to be sold.
One of the critical aspects when forming logs is control of the diameter and the quantity of wound material. In fact, in order to allow correct operation of packaging machines the logs, and therefore the rolls obtained from them, must have more or less the same diameter, i.e. coming within a relatively narrow range of tolerance. Excessive variations in the diameter of logs causes problems and blocking during subsequent packaging of the rolls.
Moreover, each roll must contain a minimum quantity of web material, equivalent to the quantity declared on the packaging. If the quantity is below the one declared sellers and manufacturers could be reported for fraud. A quantity above the nominal amount causes economic losses for the manufacturer.
Therefore, winding of logs must be controlled so that their external diameter does not differ significantly from the nominal value, obtained with a predetermined quantity of wound material or slightly above said predetermined quantity.
While in the most advanced and more costly rewinding machines these parameters are controlled accurately with sophisticated electronic systems, a problem often occurs in less costly machines equipped with limited control systems in that having set the length of the web material wound on each log, the external diameters of the various logs differ greatly. This depends on variations in thickness to which paper (especially tissue paper) is subject by nature.
U.S. Pat. No. 5,267,703 describes a rewinding machine with a winding roller with moving axis associated with a member to control movement of the roller, to ensure that a diameter contained within a predetermined range of tolerance is obtained, with a preestablished quantity of wound web material. This machine is efficient and has a limited cost. Nonetheless, it is still too sophisticated for some types of market also on account of the diameter control system used.